The past 18 years has witnessed several changes in the fire fighting industry. Foam delivery nozzles have enlarged their capacity from 500-1,000 gpm to 6,000-10,000 gpm, or higher. Fire hoses have increased in size from 21/2" diameters to 5"-10" diameters. Foam pumper capacity has gone from 1,000 gpm to 2,500-6,000 gpm. Importantly, storage tanks for flammable and combustible liquids have increased in size dramatically from 125-150 feet diameter to 300-345 feet diameters.
Fire fighting procedures in the last eighteen years have also changed. A popular historic approach to extinguish a tank fire containing combustible or flammable liquid was to "surround and drown." Too often, however, the fire did not go out. The present inventor became one of the first in the field to recognize, through the review of numerous videos of tank fires, that foam, under the "surround and drown" system, was not reaching the full surface of the tank. The apparent reason was that the fire was "breathing", and in particular, there was an area, which came to be labeled the sweet spot, where the fire was taking in air (oxygen). Adjacent this sweet spot the fire would pulsatingly flame. A combination of sweet spot, breathing and thermal drafts was driving foam back and away from the middle of the tank surface.
Experience showed that the sweet spot typically lay just off of the center of the tank, and extending upwind approximately to the tank wall. For a variety of considerations, fire fighting nozzles are also upwind of the tank. The present inventor lead the field in revising techniques so that foam came to be applied predominantly toward the sweet spot.
For every tank size N.F.P.A. specifies a minimum "application density rate." Multiplying the square foot surface of a tank times the minimum "application density rate" yields a required minimum number of gallons per minute of foam that is to be applied. N.F.P.A. also specifies a minimum application time, e.g. 65 minutes. Applying the minimum g.p.m. foam for the minimum time should extinguish a tank fire. It became the present inventor's further experience, however, that applying a minimum gpm for the minimum time did not always lead to the extinction of a tank fire, even with foam applied predominantly to a sweet spot.
The above discovery led to the present invention. The inventor can demonstrate to the industry, in contrast to conventional wisdom, that each nozzle lays down a distinct footprint of foam. Conventional wisdom only considered it significant to measure a nozzle's maximum reach. The present inventor also teaches that foam has a "maximum run" on the top of flaming fluid. Maximum run is determined empirically to be approximately 100 feet. Putting together the above two discoveries, it can be demonstrated that if predicted footprints of foam require foam to "run" over 100 feet to completely cover a tank surface then notwithstanding applying a minimum, or even well over a minimum, "gallons per minute", and regardless of directing a significant amount of foam to the sweet spot, there will be areas of the tank that will not receive foam and there is some likelihood the fire will not go out.
As a result of the above discoveries, the present inventor teaches a method for configuring nozzles at a burning tank such that they not only satisfy the minimum application density rate prescribed by N.F.P.A. and cover the sweet spot, but they also provide, taking footprints and foam run limitations into account, a foam run to all of the walls of the tank. To so configure nozzles, the inventor empirically determines a footprint for each size of nozzle potentially usable.
The inventor's method can be used in designing for a fixed placement of nozzles in a dike system, permanently installed surrounding a tank, and/or for staging mobile nozzles around a burning tank.